The present invention relates to a heat treatment apparatus for objects to be processed.
Processing of semiconductor wafers, objects to be processed, includes heat treatment steps as important ones of the steps of the processing. The heat treatments are for, e.g., formation of oxide films on the objects to be processed, diffusion of dopants, annealing, CVD, etc. Recently vertical heat treatment apparatuses are dominantly used in place of horizontal heat treatment apparatuses because of the advantage of the former that air intrusion onto the surfaces of the objects to be processed is less.
As shown in FIG. 14, the vertical heat treatment apparatus of this kind includes a vertical heat treatment furnace 11, a wafer boat 12 as a wafer holder which holds a number of wafers W arranged in a shelves-like manner at a vertical pitch, a transfer stage 13 on which a wafer carrier C (hereinafter called "carrier") to transfer the wafers W, a loading/unloading port for the carrier C; a carrier stocker, etc. The wafers W in the carrier mounted on the transfer stage 13 are transferred to the wafer boat 12 by a transfer arm 14. After a required number of wafers are mounted on the wafer boat 12, the wafer boat 12 is lifted into the heat treatment furnace 11 by a boat elevator, and a required heat treatment is conducted on the wafers W in the heat treatment furnace 11.
Because of the structure of the heat treatment furnace, the upper and lower end portions of the wafer boat 12 have lower temperatures than the rest of the wafer boat 12. To prevent inhomogeneous treatment among the wafers W, dummy wafers are placed at the upper and the lower parts of the wafer boat 12, and proper wafers are placed except at the upper and the lower end parts. As shown in FIG. 15, the wafers-to-be-processed holding region of the wafer boat 12 has lot regions P1-P4 for 4 lots each of which can include, e.g., 25 sheets of wafers. For example, in a case that wafers to be processed are transferred from 4 carriers onto the wafer boat 12, the wafers in each carrier are transferred to each lot region P1-P4. In FIG. 15, D represents dummy wafer holding regions.
On the other hand, to monitor states of a treatment conducted on the wafers-to-be-processed in each lot, product monitor wafers are heat-treated together with the wafers-to-be-processed in the lot. Product monitor wafers are stored in a carrier in the carrier stocker of, e.g., the heat treatment apparatus and are taken out of the carrier to be transferred to between the respective lot regions P1-P4 (including the holding position which is upper of the lot region P1 by one stage) in the wafer boat 12.
When product monitor wafers are used, a product monitor wafer mode switch on an operation panel of the heat treatment is pressed to transfer product monitor wafers to between the lot regions P1-P4. In this case, in the wafer holding region P1-P4 wafers to be processed are held, and product monitor wafers are held in between the lot regions P1-P4 (in the regions MA indicated by the double lines in FIG. 15). When a number of wafers in one carrier is less than 25 sheets, a lacking number of wafers is not supplemented (holding grooves of the wafer boat are left unfilled), or a lacking number of wafers is added to fill all the holding grooves.
Here, in a heat treatment apparatus with a wafer boat which can hold wafers of, e.g., four carriers, sometimes in one operation of processing, all four carriers are not used, or a number of wafers in one carrier is less than 25 sheets. In these cases, it is advantageous that the lot regions are not fixed with respect to the carriers, and those of the lot regions where the apparatus exhibits good characteristics, e.g., better intra-surface uniformity of a heating temperature are used. To this end, the inventors of the present invention proposed that when one of the holding grooves of the wafer boat is designated, all objects-to-be-processed of one batch are held in those holding grooves concentratedly (without empty ones), which are upper and lower of the designated holding groove, whereby higher freedom in degree of selection of holding positions of wafers, objects to be processed can be realized.
The heat treatment apparatus does not have always stable states and often deteriorates suddenly or gradually treatment conditions. To continue useless treatments or pause the device in normal operations, it is important to monitor states of the heat treatment apparatus. Generally it is not necessary to use product monitor wafers for every treatment when the heat treatment apparatus is sufficiently stable, and it suffice to use product monitor wafers once for several treatments. In view of this, the inventors have proposed using monitor wafers in the monitor wafer carrier as apparatus monitor wafers. The apparatus monitor wafers, however, are for checking states of the apparatus and reference levels about film thickness intra-surface uniformity and particle numbers for the apparatus monitor wafers are different from those for the product monitor wafers. Accordingly the apparatus monitor wafers are sent, after a heat treatment, to inspection steps which are different from those for the product monitor wafers.
Preferably the apparatus monitor wafers for thus monitoring states of the heat treatment apparatus are treated at set positions in a heating furnace, i.e., are held in set holding grooves of the wafer boat. In the conventional case that the lot regions are fixed, switches for, e.g., those P1, P4 of the lot regions P1-P4 on the operational panel are pressed to the apparatus monitor wafers are held in the holding grooves immediately one-stage upper of the lot regions P1, P4, whereby the apparatus can be monitored always at the set positions. In the case of the mode the inventors have proposed, when a number of wafers to be processed for one batch is smaller than a capacity number, the apparatus monitor wafers are arranged concentratedly in those of the holding grooves without empty ones in those holding grooves, a region for holding wafers-to-be-processed of one lot is varied. The conventional positioning of the monitor wafers cannot set holding locations of the apparatus monitor wafers, and as a result, disadvantageously monitored results of the apparatus are less reliable.